The long term goal of these studies is to determine the signal transduction mechanisms through which growth factors stimulate hematopoietic proliferation and differentiation. The major goal is to understand mechanisms through which erthropoietin regulates ion channels during erythroid differentiation. Bone marrow aspirates will be performed on healthy volunteers. We will address the following: electrophoresiologic characterization of the erythropoietin-regulatable calcium channel; determination of the signalling mechanisms through which erythropoietin regulates calcium channels; and exploration of differences in the signalling mechanism of erythropoietin at different stages of erythroid maturation. Differences in channel/receptor coupling will be explored with microinjection of activated alpha subunits or p21 ras.